A trojan has been discovered that infects browsers and changes users' start pages to advertising sites.

Trojan-Downloader.Acad.Qfas.b installed additional malware aimed at the popular drafting and design program AutoCAD, with the overall goal of changing browser start pages in order to drive clicks to sites of attackers' choosing.
The large amount of traffic driven to these web pages allows scammers to benefit monetarily through ads placed on them.
According to a blog post by Kaspersky Lab researcher Vigi Zhang, the threat is undetectable by a majority of anti-virus programs and has been primarily affecting users in China, India and Vietnam.